Overvoltage protection devices are available in two basic varieties, namely semiconductor devices, particularly Zener diodes and varistors, and gas discharge devices. Such overvoltage protection devices are known from "Transient Voltage Suppression Devices", Harris Semiconductor, Harris Corporation, 1990, particularly Chapter II. Different properties of different semiconductor devices and a gas discharge device are described. The semiconductor devices have is the disadvantage of a high leakage current, which results in a permanent power loss. A low breakdown voltage is difficult to implement and leads to a high leakage current. The semiconductor devices also have a relatively high depletion-layer capacitance, which results in a relatively long response time. Gas discharge devices have more favorable leakage current characteristics and, thus, a lower power loss. However, they cannot be used as low-voltage protection devices, since they can only provide overvoltage protection well above 100 V. Furthermore, gas discharge devices have a wide tolerance with respect to their rated voltage. Semiconductor devices have the disadvantage of requiring a large amount of chip area. Gas discharge devices are not suitable for integration.
The object of the invention is to provide an overvoltage protection device and a process of fabricating an overvoltage protection device which has a low leakage current and, thus, a low power loss, a short response time, and a low breakdown voltage, so that it is suitable for use as a low-voltage protection device.